Using Electrical Resistivity Imaging to Evaluate Permangante Performance During In Situ Chemical Oxidation Treatment of a RDX-Contaminated Aquifer

Site Name:

Nebraska Ordnance Plant (NOP)

Location:

Mead, Nebraska

Period of
Operation:

Permanganate injection was performed on June 19, 2007, for 8 hours. Electrical Resistivity Imaging (ERI) was used to track permanganate distribution with the final tracking period from August 29-31, 2007. Groundwater was monitored in selected wells approximately twice weekly (18 times) for the 59-day period from June 19 through August 17, 2007.

Cleanup
Type:

Field Demonstration

Technology:
In Situ Chemical Oxidation

The demonstration used in situ chemical oxidation (ISCO) to remediate contaminated groundwater at the site. ERI was used to track the distribution and flow of injected sodium permanganate. Details regarding the demonstration are provided below:

  • ISCO extraction, injection, and 11 monitoring wells were used from a previous experiment conducted at the site. Additional monitoring wells were installed in April 2007 prior to the injection.
  • Contaminated groundwater was extracted from a central well, mixed with sodium permanganate, and then gravity fed into two peripheral wells for approximately 7 hours.
  • Extracted groundwater was then recirculated to two injection wells for 42 minutes.
  • The injection rate was approximately 20.5 gallons per minute.
  • For the ERI survey, 56 steel stakes were installed at a depth of approximately 6 inches to establish electrical contact. Electrodes for two ERI lines were placed over the injection wells and oriented perpendicularly to the extraction wells.

Cleanup Authority:
Department of Defense (DoD)

Contacts:

Principal Investigator
Steve Comfort
School of Natural Resources
University of Nebraska
256 Keim Hall
Lincoln, NE 68583
Phone: 402-472-1502
Email: scomfort@unl.edu

Co-Principal Investigator
Todd Halihan
School of Geology
Oklahoma State University
105 Noble Research Center
Stillwater, OK
Phone: 405-744-6358
Email: todd.halihan@okstate.edu

Co-Principal Investigator
Vitaly Zlotnik
Geosciences
University of Nebraska
318 Bessey Hall
Lincoln, NE 68502
Phone: 402-472-2495
Email: vzlotnik1@unl.edu

Co-Principal Investigator
Mark Burbach
School of Natural Resources
University of Nebraska
512 Hardin Hall
Lincoln, NE 68583
Phone: 402-472-8210
Email: mburbach@unl.edu

Environmental Restoration Program Manager
Andrea Leeson
ESTCP Office
901 Stuart Street, Suite 303
Arlington, VA 22203
Phone: 703-696-2118
Email: andrea.leeson@osd.mil

Contaminants:
Hexahydro-1,3,5- trinitro-1,3,5-triazine (RDX)

Waste Source:
At the former NOP, which was a military loading, assembling, and packing facility, contaminated wastewater produced during ordnance manufacturing was discharged into sumps and drainage ditches; contaminants then leached into the soil and groundwater.

Type/Quantity of Media Treated:
Groundwater (approximately 70 cubic meters (m3) of groundwater in a volume of 230 m3 aquifer material)

Purpose/Significance of Application:
This demonstration was designed to evaluate the efficacy of in situ chemical oxidation (ISCO) using sodium permanganate to remediate RDX contamination and to determine the utility of electrical resistivity imaging (ERI) as a geophysical tool to characterize the effects of the ISCO remediation effort.

Regulatory Requirements/Cleanup Goals:
For the ISCO demonstration, the performance objective was to remediate RDX-contaminated groundwater to concentrations below the U.S. Environmental Protection Agency (EPA) health advisory level. For the ERI demonstration, the performance objective was to observe the temporal distribution of the injected permanganate using ERI. Quantitative performance goals include the following:

  • Reduce RDX mass by greater than 90 percent.
  • Reduce RDX concentration below EPA Health Advisory Level (2 micrograms per liter (µg/L)).
  • Achieve a root mean square (RMS) of ERI data sets less than 20 percent.

Results:
Groundwater was monitored in selected wells approximately twice weekly (18 times) for a 59-day period from June 19 through August 17, 2007. Collected samples were analyzed for permanganate and for RDX. ERI surveys were conducted one month prior to, during, and one and two months following the injection. Results for both the ISCO and ERI survey demonstrations are detailed below:

ISCO

  • The ISCO treatment reduced groundwater RDX concentrations by up to 80% (64.6 to 13.1 µg/L) but not to target levels (2 µg/L) during the demonstration period.
  • At the completion of a seven hour injection period, sodium permanganate concentration in the first extraction well had only reached 2,386 milligrams/liter (mg/L), indicating that a uniform curtain of permanganate was not established across the injection wells.


ERI
  • ERI successfully observed the appearance and movement of the injectate; however, more intense processing and analysis was needed to track the permanganate.
  • ERI data qualitatively showed that site heterogeneity directed permanganate flow away from monitoring wells in unanticipated directions, making it challenging to quantify permanganate concentration across the treatment area.
  • There was insufficient data from ERI and wells to obtain a quantitative correlation between changes in electrical resistivity and permanganate concentration.

Cost Factors:
The total cost of the ISCO pilot test demonstration was approximately $66,635. Primary cost elements included:

  • Capital Costs (including labor, materials, utilities, and instruments): $33,377
  • Operation and Maintenance: $32,428
  • Disposal of residues/well water and well cuttings: $830


The total cost of the ERI pilot test demonstration was approximately $53,377. The unit cost per sample for ERI characterization was $0.76. Primary cost elements include:
  • Capital Costs (including mobilization, planning, and equipment): $60,000
  • Operation and Maintenance: $3,915 per day
  • Data Visualization and Reporting: $1,500 per field day

Description:
The former NOP was a military loading, assembling, and packing facility that produced bombs, boosters, and shells during World War II and the Korean War. It was situated on approximately 17,250 acres and housed multiple load lines, a bomb booster assembly plant, an ammonium nitrate plant, two explosive burning areas, a proving range, a landfill, and a wastewater treatment plant. RDX was used in a variety of ordnances while TCE was used as a degreaser to clean pipelines carrying liquid oxygen fuel for missiles production. During and following ordnance production, contaminated wastewater was discharged into sumps and drainage ditches, from which contaminants leached into the soil and groundwater. Groundwater underneath and downgradient from the site has RDX concentrations as high as 534 µg/L and TCE concentrations as high as 4,800 µg/L. The size of the contaminant plume beneath the NOP was estimated to be at approximately 23 billion gallons.

In this demonstration, ISCO (using sodium permanganate) was used remediate RDX contamination. The injection was performed on June 19, 2007, for 8 hours. ERI datasets were collected one month prior to, during, and one and two months following the injection to determine if ERI was effective at tracking permanganate distribution. The ISCO demonstration quickly reduced RDX levels by 80%, but did not achieve the health advisory level of 2 µg/L. This was likely due to issues such as uneven permanganate distribution. ERI showed that the permanganate followed preferential flow paths that were not congruent with the location of the monitoring wells and rapidly moved beyond the monitoring well network. Based on the results, it was concluded that while ERI data can provide the distribution of electrical properties in the subsurface, it is not a direct substitution for well or direct push sampling data.